GB2132374A

GB2132374A - A two-dimensional acousto-optic deflection arrangement

Info

Publication number: GB2132374A
Application number: GB08233768A
Authority: GB
Inventors: John Stuart Heeks; Roger Ernest Cooke
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-11-26
Filing date: 1982-11-26
Publication date: 1984-07-04
Also published as: AU2409784A; ES527524A0; ES8500672A1; US4561727A; JPS59162527A; NO834358L; FR2537315A1; DE3342207A1

Description

1

GB 2 132 374 A 1

SPECIFICATION

A two-dimensional acousto-optic deflection arrangement

This invention relates to a two-dimensional 5 acousto-optic deflection arrangement and is suitable for a thermo-optically addressed liquid crystal display (LCD) device.

A thermo-optic liquid crystal display cell filled with a smectic liquid can be used to form a 10 projection system in which a focussed laser beam is employed to write a pattern on a plain background. If the cell is constructed to confine a thin layer of liquid crystal exhibiting a smectic phase, and the two major interior surfaces of the 15 cell are treated to promote homeotropic alignment of the liquid crystal molecules adjacent those surfaces, then the visual clarity of such a layer in the isotropic liquid phase is preserved if it is first heated and then slowly cooled to transform it into 20 the smectic phase. This clarity is preserved in the smectic phase because the slow rate of cooling enables the liquid crystal molecules to assume homeotropic alignment. If the two major interior surfaces are also provided with the transparent 25 electrode coatings so that an electric field can be applied across the thickness of the liquid crystal layer then, by the application of a suitable a.c. electric field, the rate of cooling may be increased. This complete homeotropic alignment state is 30 effectively a visually plain field or background. Substantially distinctive lines can then be written on to this plain field by tracking a focussed laser beam across the surface of the liquid crystal layer at an appropriate rate, and in the absence of an 35 electric field, to supply sufficient energy to the regions successively illuminated by the focussed beam to result in a scattering state remaining after rapid cooling of the locally heated regions of the liquid crystal material. Such a mechanism is 40 disclosed in U.S. patent 3,796,999.

According to the present invention there is provided a two-dimensional acousto-optic deflection arrangement including a source of electromagnetic radiation, means for modulating 45 the source, means for collimating the output of the source into a beam, an acousto-optic deflection means situated in the path of said beam, the deflection means comprising a rectangular body of acousto-optic material provided on two adjacent 50 surface with electro-acoustic transducers arranged to launch orthogonal bulk acoustic waves into the material transverse the direction of propagation of radiation through the material whereby the collimated radiation can be scanned 55 in two dimensions over a predetermined area. Embodiments of the invention will now be described with reference to the accompanying drawings, in which:—

Figure 1 illustrates a simple deflector 60 arrangement,

Figure 2 illustrates in schematic form a two-dimensional acousto-optic deflector arrangement with secondary illumination, and

Figure 3 illustrates in schematic form an

65 alternative arrangement to that of Figure 2.

In the arrangement shown in Fig. 1 a source 10 of electromagnetic radiation, e.g. a semiconductor junction laser, has its output collimated by a first lens 11 into a parallel beam. A rectangular body 70 12 of acousto-optic material, e.g. lithium niobate or tellurium dioxide has electro-acoustic bulk wave transducers 13, 14 on adjacent surfaces arranged to launch bulk waves into the material transverse the direction of propagation of the 75 beam through the body 12 whereby deflection of the emergent radiation can be effected independently in two orthogonal directions x, y. Finally, the emergent radiation is focussed by a second lens 15 to a spot at the required distance. 80 Thus by suitable energising of the transducers 13 and 14 the spot of light can be scanned in either a raster or random access manner across a surface.

In the arrangement shown in Fig. 2 the light from a laser source 10a is scannable via optics 85 11 a, 15a, 2-dimensional bulk wave deflector 12a and e.g. a partially silvered mirror 16 across the face of a thermo-optically addressable liquid crystal cell 17. The output of the laser source 10a is controlled by a modulator 18 which also 90 controls the deflector 12a. The cell 17 may be first subjected to heating and cooling in the presence of an electric field as previously described to induce an overall homeotropic state. The output of the laser may then be modulated and the 95 modulated beam 19 scanned across the cell surface in the absence of an electric field to "write" in information to be displayed in the form of a substantially distinctive pattern. A source of secondary illumination 20 is then arranged to 100 illuminate, via the partially silvered mirror 16, the cell 17 so that the written-in pattern can be projected via optics 21 onto a screen 22. Typically the laser source 10a is a GaAIAs laser.

It will be appreciated that the positions of the 105 laser source 10a etc and the secondary illumination lamp 20 may be interchanged.

In the alternative arrangement shown in Figure 3 there is no half-silvered mirror. Instead the laser 10a and lamp 20 are side by side, one or each 110 slightly offset with respect to the cell 17. The degree of misalignment is small enough to permit effective writing-in of information and subsequent illumination of the cell. Additional optics 23 may be included in the secondary illumination path if 115 required.

Whilst the main feature of the invention has been described so far only in the context of a display it is also applicable in other fields. For example the deflection arrangement may be 120 suitable for writing information or patterns on photosensitive surfaces generally. Applications such as pattern forming on a photoresist layer for manufacture of printed circuits, or for writing on photosensitive paper which is subsequently 125 treated to fix the images, are envisaged.

Claims

1. A two-dimensional acousto-optic deflection arrangement including a source of

2

GB 2 132 374 A 2

electromagnetic radiation, means for modulating the source, means for collimating the output of the source into a beam, an acousto-optic deflection means situated in the path of said beam, the 5 deflection means comprising a rectangular body of acousto-optic material provided on two adjacent surfaces with electro-acoustic transducers arranged to launch orthogonal bulk acoustic waves into the material transverse the direction of

10 propagation of radiation through the material whereby the collimated radiation can be scanned in two dimensions over a predetermined area.

2. An arrangement according to claim 1 including a source of secondary illumination

15 arranged to illuminate said predetermined area.

3. An arrangement according to claim 2 wherein the source of electromagnetic radiation and the source of secondary illumination are disposed with their outputs orthogonal to one

20 another, the arrangement including mirror means for combining the outputs arranged to deflect one of said outputs to be colinear with the other output.

4. An arrangement according to claim 2 or 3

25 including a thermo-optically addressable liquid crystal display device positioned so as to be scannable by the deflected focussed radiation and illumination by said source of secondary illumination.

30

5. An arrangement according to any preceding claim wherein the source of electromagnetic radiation is a GaAIAs laser.

6. A two-dimensional acousto-optic deflection arrangement substantially as described with

35 reference to Fig. 2 of the accompanying drawings.

7. A thermo-optically addressable liquid crystal display including a two dimensional acousto-optic deflection arrangement as claimed in claim 1,

2 or 3.

40

8. A visual display equipment incorporating a two-dimensional deflection arrangement as claimed in one of claims 1—6.

9. Apparatus including a two-dimensional deflection arrangement as claimed in claim 1 for

45 transferring images to a photosenstive surface.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1984. Published by the Patent Office. 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.